Concerning Coplaintiffs terminating relationship... im not sure of the details. Another coplaintiff left the lawsuit early on, before any settlement was offered.
I suggest you discuss the settlement with your attorney/the new attorney to see if the current settlement can be saved or if another one can be worked out to everyone's satisfaction.
Your attorney is handling the case like a class action suit (without the class certification). Outside a class action, it often can be best for all plaintiffs to be represented by their own attorneys. Your attorney is trying to juggle the interests of 5 different clients. Although their interests may be similar, they are not identical.
I suggest you look for the attorney contract you signed, and any additional "common interests" agreement that might have been signed, and ask all questions you have on Saturday when you meet with the new attorney.
Good luck.